1. Field of the Invention
The present invention pertains to non-ferrous foundry arts, and more particularly a pouring ladle for transferring molten non-ferrous metal from a melting furnace to a casting mold.
2. Description of the Prior Art
FIG. 1 shows a pouring ladle 10, usually constructed of steel, in cross section having a refractory lining in the range of one to two inches thick applied over the entire internal surface of the ladle. The refractory lining may be of any appropriate material such as zircon refractory material which is well known in this art. The combination of the ladle and refractory lining shown in FIG. 1 is old art and is discussed here to show the current manner in which a steel pouring ladle is provided protection from a non-ferrous melt such as molten aluminum poured therein.
The ladle assembly of FIG. 1 requires a heavy preheat prior to pouring a non-ferrous melt therein. A steel ladle weighing about one thousand pounds is capable of transporting about one thousand pounds of aluminum in liquid phase and requires a preheat for about one hour using a flame supported by about fifteen hundred cubic feet of gas per hour. The preheat brings the interior of the ladle assembly of FIG. 1 up to the range of 500 to 700 degrees Fahrenheit and is undertaken for the purpose of driving off as much mechanically and chemically held moisture as possible from the lining prior to introducing the melt into the ladle. It is not possible to drive off all of the moisture from the refractory material 11 as there are compounds such as aluminum oxide, magnesium oxide and aluminum chloride among others which are formed in the presence of melted aluminum and which adhere to the refractory material once it is exposed to an aluminum melt. The aforementioned compounds are hygroscopic in nature and appear to hold molecular hydrogen and water chemically. The combinations which appear to be readily formed when melted aluminum is handled by usual foundry practices are collectively termed dross, which is equivalent to slag in the terminology associated with ferrous metal foundry practices, and which is scattered throughout the body of the aluminum melt. That dross which is left behind by a melt on the walls of the refractory material is extremely difficult to remove prior to pouring a subsequent melt in the ladle assembly of FIG. 1 and a higher concentration of dross is noticed in subsequent pourings. This results in increased outgassing from the refractory material as a skull or layer containing the undesirable compounds collects at the surface of the ladle. The result is observed in what are termed gassy castings of comparatively low quality. The skull is readily formed on the refractory material surfaces with each melt poured into the ladle because the refractory material is easily wetted by the melt.